The present invention relates to a sputtering apparatus for performing sputtering by magnetron sputtering method using a target made of ferromagnetic material to form a thin film such as a thin film used in a magnetic recording head for a VTR.
Sputtering method is used to generate plasma by giving rise to gas discharge in an atmosphere of a low degree of vacuum so that positive ions of the plasma collide with a target mounted on a negative pole called as a cathode. Particles sputtered by the collision between the positive ions and the cathode are deposited on a substrate to form a thin film. Sputtering method is widely used in a film forming process because the control over the composition of the film and the operation of an apparatus can be performed comparatively easily. But sputtering method has a disadvantage that the thin film forming speed thereof is lower than that of vacuum evaporation. In order to solve the disadvantage, magnetron sputtering method has been devised to form a magnetic field in the vicinity of the target by using permanent magnets or electromagnets as a magnetic circuit. Magnetron sputtering method has allowed the thin film forming speed of the apparatus to be higher and thin films to be mass-produced on substrates of semiconductor components and electronic components.
Magnetron sputtering method has, however, a disadvantage that a film formed on a substrate has a nonuniform thickness and hence a poor quality due to a local corrosion of the target. In order to solve the disadvantage, an apparatus for forming a uniform magnetic field perpendicular to an electric field has been devised.
An example of a conventional sputtering apparatus is described below with reference to FIG. 12 which is a sectional view showing the construction thereof. In FIG. 11, there are provided a chamber 1; an evacuation port 2 communicating with a vacuum pump; a gas introducing pipe 3; a gas flow rate controller; electric discharge gas 5 consisting of argon; a target 6; a sputtering electrode 7; an electric discharge power supply 8; magnet holders 9; magnets 10; a substrate holder 11; and a substrate 12 on which a thin film is formed.
The operation of the sputtering apparatus having the above-described construction is described below. The chamber 1 is evacuated from the exhaust port 2 at a degree of approximately 10.sup.-7 Torr. Then, the discharge gas 5 is introduced into the chamber 1 via the gas introducing pipe 3 connected with an end of the chamber 1 to keep the pressure in chamber 1 at approximately 10.sup.-3 -10.sup.-2 Torr. A negative voltage or a high frequency voltage is applied to the sputtering electrode 7 mounted on the target 6 by the DC or AC discharge power supply 8. As a result, plasma is generated in the vicinity of the front surface of the target 6 owing to discharge caused by the action of an electric field generated by the power supply 8 and a magnetic field generated by the magnets 10 accommodated in the magnet holders 9. Consequently, sputtering phenomenon occurs, i.e., particles sputtered from the target 6 are deposited on the substrate 12 mounted on the substrate holder 11 to form a thin film.
In the sputtering apparatus, most of magnetic fluxes generated by the magnets 10 passes through the target 6 if the target 6 is made of ferromagnetic material. Thus, the number of magnetic fluxes which contribute to the formation of plasma is small. As a result, the film forming speed is low.